Linkages are used in a wide variety of applications. For example, vehicles such as lawn mowers may include linkages adapted to manipulate specific components of the mower. Such mowers may be configured as either walk-behind or ride-on (stand-on or sit-on) units. For ride-on and larger walk-behind mowers, zero-turning-radius (ZTR) functionality is often provided.
A ZTR mower generally includes a prime mover (e.g., internal combustion engine or electric motor) coupled to a continuously variable (e.g., hydraulic) transmission drive system. The drive system may include left and right hydraulic motors coupled to left and right drive wheels, respectively. Power may be transmitted from the prime mover to the left and right hydraulic motors, e.g., via one or more pumps, to drive the left and right drive wheels independently. The rotational speed and direction of each drive wheel may then be controlled by an associated drive control lever under the control of an operator.
Each drive control lever may typically be positioned at any location between a neutral and a full forward (or a full reverse) position to proportionally alter the speed of the associated drive wheel. A stop may define the full forward position of each control lever (while a second stop may define the full reverse position), and both levers are typically biased to the neutral position.
During mower operation, the operator may seek to place the control levers in the full forward position as this position allows resting of the levers against the stop. This may offer the operator increased comfort, as well as reduce inadvertent lever movement as a result of, for example, traversal of undulating terrain. However, due to variability and tolerances in the manufacture and assembly of mower components (e.g., slight differences in the efficiency of the hydraulic pumps and motors, variations in the lengths of linkage components, variations in tire pressure, etc.), it is not uncommon for one wheel to track faster than the other when both drive control levers are in the full forward position.
To address this issue, the linkages connecting the levers to the drive transmissions may be adjusted. While effective in equalizing the maximum forward speed of each drive wheel, this adjustment may shift one of the levers such that its neutral position is slightly offset (e.g., at a more forward location) from that of the other lever. As a result, when both levers are then moved to the full reverse position, one lever may actually travel farther than the other, resulting in the associated drive wheel rotating faster (in reverse) than the other drive wheel.